Learning The Calendar

This is one of the brain improvement which you can use to amuse your friends! Learning the calendar means to know what day it is every time you see a date. When your friends ask you what day is it on 1 January 1987, you'll be able to tell them that it's Thursday!
Other examples:
3 March 1865 : Friday
27 October 2066: Wednesday

Your friends will definitely say, how did you do that?!

It's easy, but it's also difficult. I mean, you have to memorize the codes first, then you can amuse your friends! There are some codes to memorize.

For the explanation, I will use the date 29 May 2057

There are 3 things you get from a date: day, month, year, and century. Thus, there are 4 kinds of codes:

1. Day Code
   The day code is easy, in fact, you don't have to memorize anything! We are working with the basis 7 here, so subtract the day number by 7 until it can't be subtracted again.
   Example: 29 you get from 29 May 2057, subtracted by 7 for 4 times leaves you with 1. So here, the code is 1.
   
   
2. Month Code
   Here, you have to memorise the code for each month:
   
   1. January : 1
   2. February : 4
      
   3. March : 4
   4. April : 0
   5. May : 2
   6. June : 5
   7. July : 0
   8. August : 3
   9. September: 6
   10. October : 1
   11. November : 4
   12. December : 6
   For the example, it is May, so the month code is 2.
   
   
3. Year Code
   Year code is the most important part of this method. You have to memorize the code for each year, to make it easier, I divide them into 7 categories:
   I will present them just straight to the year, for example: 57, 68, 99
   
   Year code: 0
   The year: 00, 06, 17, 23, 28, 34, 45, 51, 56, 62, 73, 79, 84, 90
   
   Year code: 1
   The year:01, 07, 12, 18, 29, 35, 40, 46, 57, 63, 68, 74, 85, 91, 96
   
   Year code: 2
   The year: 02, 13, 19, 24, 30, 41, 47, 52, 58, 69, 75, 80, 86, 97
   
   Year code: 3
   The year: 03, 08, 14, 25, 31, 36, 42, 53, 59, 64, 70, 81, 87, 92, 98
   
   Year code: 4
   The year: 09, 15, 20, 26, 37, 43, 48, 54, 65, 71, 76, 82, 93, 99
   
   Year code: 5
   The year: 04, 10, 21, 27, 32, 38, 49, 55, 60, 66, 77, 83, 88, 94
   
   Year code: 6
   The year: 05, 11, 16, 22, 33, 39, 44, 50, 61, 67, 72, 78, 89, 95
   
   For this example: 2057 means that the number is 57 with the code 1.
   
   
4. Century Code
   For the century code, it has a series: 6, 4, 2, 0, ...
   Starting from 1600s : 6
   1700s : 4
   1800s : 2
   1900s : 0
   2000s: 6
   and so on...
   For this example: 2057 means that it's in the 2000s with the code 6.
   

To sum up: 29 May 2057 has the code:
Day code: 1
Month code: 2
Year code: 1
Century code: 6
Sum the codes you have : 1 + 2 + 1 + 6 = 10
Again, we are working with the basis 7, so subtract all 7s, that leaves you with 3.

Translation code:
1 : Sunday
2 : Monday
3 : Tuesday
4 : Wednesday
5 : Thursday
6 : Friday
0 : Saturday

Thus, 29 May 2057 falls on Tuesday!

Leap Year:
For leap years, subtract 1 from the total.
IMPORTANT : Do this only when the date is between 1 January and 29 February!

Example: 24 January 1912
Day code : 3
Month code : 1
Year code : 1
Century code : 0
TOTAL: 5
It is a leap year. Thus, subtract 1:
The total is 4, means that it's Wednesday!

I think that's all, just memorize those codes and you'll be ready to amuse your friends in no time!
Good luck!